Related fields include thin-film microwave devices with superconducting components and passivation processes for dielectrics.
At temperatures <100 mK, amorphous silicon (a-Si) is a dielectric. Its low cost and ease of fabrication make it attractive as an interlayer dielectric (ILD) for superconducting interconnects and components for planar microwave devices, but its loss tangent (˜108) is much larger than that of single-crystal Si (˜107) at microwave frequencies (e.g., 3-300 GHz) and longer infrared frequencies (300-1000 GHz). The loss tangent is believed to be caused by defects occurring during deposition. A lower loss tangent would benefit high-frequency classical devices by reducing signal attenuation, dispersion and jitter. A lower loss tangent would benefit quantum devices, such as rapid single flux quantum (RFSQ) circuits and reciprocal quantum logic (RQL) by increasing coherence times for quantum state signals.
Crystalline dielectrics are observed to have lower loss tangents than their amorphous counterparts. However, crystallization of interlayer dielectrics for superconducting circuits typically requires temperatures high enough to cause unwanted reactions between the dielectric and the wiring materials (e.g., Al or Nb). Hydrogenation has been observed to improve a-Si loss tangent in some cases. However, ILD layers are typically 300-1000 nm thick. At this thickness, many surface treatments are ineffective to remove defects from the bulk of the film. This is also an inconvenient thickness to form by the precisely controlled methods of atomic layer deposition (ALD); each ALD cycle creates a monolayer on the order of 0.1 nm thick, therefore a layer hundreds of nm thick would take too long to be cost-effective.
Therefore, a need exists for methods to reduce the microwave-frequency loss tangent of a-Si films by reducing or eliminating defects in the bulk of micron-scale films as well as on the surface.